I am using both 100 micron and 20 micron thick films with around 200
micron sized features.
The dimension of the top portion is much greater than the mask (in
both film thicknesses) leading me to believe that the exposure dose is
not the cause although I certainly do agree that a much higher dose is
generally required than specified in the datasheets.
Cheers

Gareth

On Mon, Jul 28, 2008 at 14:57, Andrew Sarangan  wrote:
> How thick is the SU-8 you are using, and what are the sizes of your features?
> I have encountered this problem in SU-8 due to under-exposing the
> resist. One way to check this is to verify the dimension of the top
> part of the exposed structure. If it is the same as the mask size,
> then you have an under-exposed lower portion. I have also found the
> dose specified on the spec sheet to be on the low side. If your
> features are large, then it doesn't hurt to over-expose.